Amplifier arrangements are widely used, for example as low-noise amplifiers in radio-frequency receiver arrangements. Depending on the power level of an incoming signal, it can be desirable to provide an amplifier with adjustable gain.
Usually, transistors are used for signal amplification. An amplifying transistor can be connected in common-emitter configuration. This results in relatively high gain, a low noise-figure and fairly good linearity when processing low level input signals.
In order to improve the linearity of an amplifier based on a common-emitter transistor configuration, it is possible to use degeneration. This is performed by connecting an inductor between the emitter terminal of the transistor and ground potential. When processing high-frequency signals, this results in a considerable improvement in linearity.
However, due to the fact that an inductor having a relatively large value is required, this inductor, due to its size, normally is an external component. In each case, the inductive degeneration requires either a relatively large chip area to integrate an inductor or an additional pin at an integrated circuit comprising the amplifier to connect an external, discrete inductor, resulting in higher costs.